package br.org.game.nio.core.udp;

import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.channels.DatagramChannel;
import java.util.Date;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;

public class TimeClient {

	private static final int DEFAULT_TIME_PORT = 9090;
	private static final long DIFF_1900 = 2208988800L;

	protected int port = DEFAULT_TIME_PORT;
	protected List<InetSocketAddress> remoteHosts;
	protected DatagramChannel channel;

	public TimeClient(String[] argv) throws Exception {

		if (argv.length == 0) {
			throw new Exception("Usage: [ -p port ] host ...");
		}

		parseArgs(argv);

		this.channel = DatagramChannel.open();
	}

	protected InetSocketAddress receivePacket(DatagramChannel channel, ByteBuffer buffer) throws Exception {
		buffer.clear();

		// Receive an unsigned 32-bit, big-endian value
		return ((InetSocketAddress) channel.receive(buffer));
	}

	// Send time requests to all the supplied hosts
	protected void sendRequests() throws Exception {
		ByteBuffer buffer = ByteBuffer.allocate(1);
		Iterator<InetSocketAddress> it = remoteHosts.iterator();

		while (it.hasNext()) {
			InetSocketAddress sa = it.next();

			System.out.println("Requesting time from " + sa.getHostName() + ":" + sa.getPort());

			// Make it empty (see RFC868)
			buffer.clear().flip();

			// Fire and forget
			channel.send(buffer, sa);
		}
	}

	// Receive any replies that arrive
	public void getReplies() throws Exception {
		// Allocate a buffer to hold a long value
		ByteBuffer longBuffer = ByteBuffer.allocate(8);

		// Assure big-endian (network) byte order
		longBuffer.order(ByteOrder.BIG_ENDIAN);
		// Zero the whole buffer to be sure
		longBuffer.putLong(0, 0);
		// Position to first byte of the low-order 32 bits
		longBuffer.position(4);

		// Slice the buffer; gives view of the low-order 32 bits
		ByteBuffer buffer = longBuffer.slice();
		int expect = remoteHosts.size();
		int replies = 0;

		System.out.println("");
		System.out.println("Waiting for replies...");

		while (true) {
			InetSocketAddress inetSocketAddress = receivePacket(channel, buffer);

			buffer.flip();

			replies++;

			printTime(longBuffer.getLong(0), inetSocketAddress);

			if (replies == expect) {

				System.out.println("All packets answered");

				break;
			}

			// Some replies haven't shown up yet
			System.out.println("Received " + replies + " of " + expect + " replies");
		}
	}

	// Print info about a received time reply
	protected void printTime(long remote1900, InetSocketAddress sa) {
		// local time as seconds since Jan 1, 1970
		long local = System.currentTimeMillis() / 1000;
		// remote time as seconds since Jan 1, 1970
		long remote = remote1900 - DIFF_1900;
		Date remoteDate = new Date(remote * 1000);
		Date localDate = new Date(local * 1000);
		long skew = remote - local;

		System.out.println("Reply from " + sa.getHostName() + ":" + sa.getPort());
		System.out.println("  there: " + remoteDate);
		System.out.println("   here: " + localDate);
		System.out.print("   skew: ");

		if (skew == 0) {
			System.out.println("none");
		} else if (skew > 0) {
			System.out.println(skew + " seconds ahead");
		} else {
			System.out.println((-skew) + " seconds behind");
		}
	}

	protected void parseArgs(String[] argv) {
		remoteHosts = new LinkedList<InetSocketAddress>();

		for (int i = 0; i < argv.length; i++) {
			String arg = argv[i];

			// Send client requests to the given port
			if (arg.equals("-p")) {
				i++;
				this.port = Integer.parseInt(argv[i]);
				continue;
			}

			// Create an address object for the hostname
			InetSocketAddress sa = new InetSocketAddress(arg, port);

			// Validate that it has an address
			if (sa.getAddress() == null) {
				System.out.println("Cannot resolve address: " + arg);
				continue;
			}

			remoteHosts.add(sa);
		}
	}

	public static void main(String[] argv) throws Exception {
		TimeClient client = new TimeClient(argv);
		client.sendRequests();
		client.getReplies();
	}

}
